This application is based upon and claims benefit of priority of Japanese Patent Application No. 2000-123848 filed on Apr. 25, 2000, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a navigation device for use in an automotive vehicle, and more particularly to a navigation device having a function to give route guidance to a driver every time a vehicle approaches a branching point, especially a junction, located on a planned route.
2. Description of Related Art
A navigation device for an automotive vehicle, which locates a present position of a vehicle, sets a route plan and gives route guidance to a driver, is known hitherto. Usually, the located present position of the vehicle and the planned route toward destination are displayed on a display panel. It is also known to give voice guidance to a driver when a vehicle approaches a branching point on the planned route. For example, voice guidance such as xe2x80x9cturn to right at an intersection 50 meters aheadxe2x80x9d is given to the driver. Such voice guidance is not given at all branching points, but it is given at particular branching points where it is difficult for the driver to correctly follow the planned route without such guidance. For example, if a minor road is simply connected to a main road and the driver can easily enter the main road on the planned route without guidance, no guidance is given.
On the other hand, the guidance is given at a branching point such as a junction where a road entering the junction branches out into two or more roads outgoing from the junction. For example, if the outgoing road toward destination has the same road name as the entering road, a voice guidance, such as xe2x80x9ccontinue to proceed to the present roadxe2x80x9d or xe2x80x9ckeep driving on the same roadxe2x80x9d is given to the driver.
The above situation will be further explained, taking an example in Japan where a left-side driving system is employed. If there are two lanes on a highway including an expressway, slow traffic moves on the left lane and the right lane is a speed lane. When a driver approaches a junction where a road toward his destination is directed to the right side of the junction, he drives on the right lane on the road entering the junction. If the entering road has the same name as the outgoing road toward his destination, voice guidance such as xe2x80x9ckeep driving on the same roadxe2x80x9d would be appropriate. However, there is another situation where the outgoing road toward his destination has the same name as the entering road another outgoing road is directed to the right side of the junction. In this case, if the voice guidance such as xe2x80x9ckeep driving the same roadxe2x80x9d is given, it is possible for the driver to proceed to the wrong road branching out to the right side from the junction. If the driver is very familiar to the structure of the particular junction, he may not be misled. However, there is a possibility in the conventional navigation device to mislead the driver.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved navigation device which is able to give a driver appropriate route guidance at a branching point, especially at a junction.
A navigation device for use in an automobile vehicle is mainly composed of a vehicle position detector including a GPS receiver, a map data feeder, a keyboard, a display panel and a speaker. A driver inputs his destination at a starting point. The navigation device sets a route plan from the starting point to the destination on the map displayed on the display panel. When the vehicle approaches a branching point, especially a junction, located on the route plan, the navigation device instructs the driver to which direction to drive. At a junction, one road entering the junction branches out into tow or more roads outgoing from the junction including an outgoing road toward destination.
The navigation device determines whether the entering road has the same name as that of the outgoing road toward destination, whether a traffic system is a left side driving system or a right side driving system, and whether at which side of the outgoing road toward destination the other outgoing roads are located. The instructions to which direction to drive are generated based on those determinations. Under the left side driving system as in Japan, if the outgoing road toward destination has the same name as the entering road, the navigation device instructs to drive to the left if the other outgoing roads are located at the right side of the outgoing road toward destination and to drive straight if the other outgoing roads are located at the left side. Under the right side driving system as in the U.S.A., the navigation device instructs to drive to the right if the other outgoing roads are located at the left side and to drive straight if the other outgoing roads are located at the right side.
If the outgoing road toward destination has a name different from that of the entering road, it is not necessary to give special instruction as above, because the driver is properly guided by usual instructions. It is preferable to give the driver the instructions by means of voice guidance in addition to the route plan displayed on the display panel. The route guidance process performed in the navigation system may be stored in a memory medium as a computer program.
A driver is properly guided by the navigation device according to the present invention because instructions to which direction to drive through a junction are generated, not only based on a physical structure of the junction and road names but also based on a customary way of driving. Under the left side driving system, a driver usually keeps right when he drives through a junction if an outgoing road toward destination has the same name as the entering road. Therefore, if the outgoing road toward destination extends leftward under such situation, the instructions to drive to the left are very helpful to the driver. On the other hand, if the outgoing road toward destination is located at the right side of the junction, the instructions to drive straight lead the driver to the proper direction. The same is applicable to the right side driving system though the left and the right are reversed.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.